Two arm robots or x, y, z positioning systems are increasingly used in test equipment for moving test probes to test positions across circuit boards. In such systems, when the arms are driven at different speeds along a common path, there is the danger that the arms, or the test probes attached to the arms, may collide resulting in significant damage.
This problem is avoided in equipment manufactured by Anorad Corporation in which both arms are slowed down without regard to the direction of movement whenever the arms are within a certain distance of each other. This results in much greater move times for long moves whenever the spacing between the arms stays small during the move. It has also been suggested that, in cases which could result in collisions, the arms be moved one after the other; but this also increases move times.
Another collision avoidance system is shown in U.S. Pat. No. 3,053,948 which proposes the use of detector wires forming a protective detector envelope or cage to actuate a switch upon engagement with an obstruction to stop all drive motions. U.S. Pat. No. 3,967,242 uses a visual sensor to cause retraction of the working unit whenever an obstacle is detected. The system shown in U.S. Pat. No. 4,332,989 operates after the fact: a collision responsive switch causes shutdown or retraction of the moved parts. All of these systems thus cause a disruption of operation in response to an incipient or actual collision.